The purpose of the lesson, which was to prepare students for pre-algebra, was made clear by the teacher. However, as the lesson proceeded, the teacher explained that the students could use the pan-balance to replace objects with other variables. These variables could be used in working out uncomplicated algebraic expressions. The flow of the lesson deviates from the key purpose. This creates an element of contradiction from the initial purpose of the study. At the end of the lesson, the students had learnt on replacements other than understanding the key concepts of pan balance and pre-algebra.

The teacher is ...